Position monitoring facility

ABSTRACT

A pumping apparatus including a pump housing, a plunger operatively coupled to a terminal end of a production string and configured to move upward and downward within the pump housing, a surface pumping unit operatively connected to an upper end of the production string, and at least one element of incremental resistance disposed on an inner surface of the pump housing or an outer surface of the plunger proximate an upper or lower limit of a pump stroke is disclosed. A method for pumping fluid from a wellbore using a pumping system having an element of incremental resistance disposed near at least one of an upper end of a pump stroke and a lower end of a pump stroke to increase the axial load is also disclosed.

BACKGROUND

Typically, wells employ a pump system configuration for extracting oil and gas from the earth. A conventional oil well pump system incorporates a down hole pump, a solid sucker rod extending from the down hole pump to the surface and a surface pumping unit, for example, a pump jack, at the surface attached to the upper end of the solid sucker rod for reciprocating the sucker rod and activating the downhole pump. An example of such conventional pump system is shown in FIG. 1A.

In pump system (100), a wellbore casing (101) extends downward from the surface to various production formations (105). Casing (101) is a tubular that lines the inside of the wellbore and includes perforations (110) in the region of the various production formations (105) that allow fluids from the formations to enter the wellbore. The casing may be a steel casing. A tubing string (102) is located within the casing (101). The tubing string may be a coiled tubing, a threaded tubing, or any other suitable type of tubing. The tubing string (102) extends downward from a well-head (not shown) to the formations. A plunger (104) is located at the terminal end of the tubing string. The plunger resides in a pump housing (106) and is operatively connected to a solid sucker rod (103). The sucker rod (103) is operatively connected to surface pumping unit (108). The surface pumping unit (108) is configured to raise and lower the sucker rod (103) to move the plunger (104) in relation to the pump housing (106) and casing (101). The plunger motion, together with the operation of the check valves (107), causes the transfer of fluids from below the plunger (104) to the annulus between the sucker rod (103) and the tubing string (102). Reciprocating motion of the plunger (104) induced by the raising and the lowering of the sucker rod (103) transfers sufficient fluid to fill the tubing string (102) and forces fluid to flow from the well to the surface.

FIG. 1B shows an enlarged cross-section view of the subsurface pump housing (106), plunger (104) and check valves (107). The check valves (107) are used to prevent backflow of fluid.

Another pump system configuration, as described in U.S. Pat. No. 6,502,639 which is hereby incorporated, eliminates the use of solid connectors, such as solid sucker rod and/or threaded tubing string. Instead, the surface pumping unit and the downhole plunger can be operatively connected using a production string. Such production string may include a hollow rod string and/or coiled tubing string. Fluid flow can be induced by using the surface pump to raise and lower the production string within the housing in a reciprocating motion in order to move the plunger between an upper and a lower end of the pump stroke.

The plunger position within the housing may be adjusted by changing the grip of the surface pumping unit along the length of the production string. For example, by raising or lowering the pump grip along the length of the production string, the upper and lower ends of the plunger stroke within the housing can also be raised or lowered for the same amplitude stroke. Further, the amplitude of the stroke may be adjusted by modifying parameters of the surface pumping unit. For example, if the surface pump is a beam pump, the amplitude of the upward and downward beam motion may be modified in order to adjust the amplitude of the downhole stroke of the plunger, which is connected to the beam by the production string.

Various types of string may be used to couple the downhole pump with the surface pumping unit. The main structural differences between the conventional solid strings, including sucker rods, and the alternative strings, including hollow rod strings and coiled tubing strings, are elasticity and flexibility. For example, coiled tubing string is continuous, flexible, elastic pipe which can be unwound from a spool as it is fed into the well. On the other hand, sucker rods consist of fixed lengths of solid pipe with threaded ends that allow the rods to be coupled together to form the solid connector.

In particular, one distinguishing feature of the hollow rod strings and coiled tubing strings over the solid sucker rods is the elastic behavior in response to axial loads. For example, hollow rod strings and coiled tubing strings may elastically stretch and/or compress more when subjected to the reciprocating motion during the pumping.

Both the pump systems using solid sucker rods, and the pump systems using hollow rod strings and/or coiled tubing strings as the production string operate in a similar fashion by reciprocating the plunger between an upper end of the stroke and a lower end of the stroke in order to pump the fluid. In both types of pump systems, monitoring and adjusting of the downhole location of the plunger are required. Such monitoring and adjusting can be used to ensure high operating efficiency of the pump system, to maintain steady pumping rates, and to prevent physical damage to the equipment. For example, the plunger location during pumping can be adjusted based on monitoring results by changing the pump grip along the length of the solid sucker rod or the production string at the surface or by changing the stroke length of the surface pumping unit.

Monitoring the plunger location in pump systems that use solid sucker rods is more straight forward than in pump systems with hollow sucker rods or coiled tubing, as the rod moves more synchronously with the surface pumping unit and exhibits less elastic stretching behavior. Further, a wide knowledge base has been developed over the years to determine downhole behavior of pump systems using conventional sucker rods. Thus, existing process models can be used to determine the downhole location of the plunger at any point during the pumping cycle.

In contrast, monitoring the downhole behavior of the conventional plunger in pump systems that use production strings, such as hollow rod strings or coiled tubing strings, may be a difficult task. Rod strings and coiled tubing strings behave differently from solid rods with comparable cross-sections during the pumping. As discussed above, hollow rod strings and coiled tubing strings can elastically stretch and/or compress significantly under axial loads during the pumping. Therefore, the plunger attached to the terminal end of the hollow rod string or coiled tubing string moves asynchronously with the surface pump throughout the pump cycle. Field tests performed on such pump systems indicate a lack of understanding of the downhole behavior of plunger. Further, the existing models developed for pump systems using solid rods fail to accurately determine the downhole location of the plunger with hollow production strings.

Therefore, there exists a need for a pump system using a production string, such as a hollow rod string or a coiled tubing string, that includes a robust and reliable system and method for monitoring the downhole location of the plunger during the pumping.

SUMMARY

In one aspect, embodiments disclosed herein relate to a system for pumping fluid including a production string having an upper end and a lower terminal end, at least one strain gauge for measuring an axial load on the production string, a pump housing comprising a plunger fixed to the lower terminal end of the production string, wherein the plunger is configured to move upward and downward within the pump housing in a pumping motion, a surface pumping unit operatively connected to the upper end of the production string, wherein the surface pumping is configured to move the plunger within the pump housing in the pumping motion between an upper end of a pump stroke and a lower end of a pump stroke, and at least one element of incremental resistance for increasing the axial load near at least one of the upper end of the pump stroke and the lower end of the pump stroke.

In another aspect, embodiments disclosed herein relate to a method for pumping fluid from a wellbore using a pumping system, the method including inserting a housing comprising a plunger coupled with a production string into the wellbore, wherein at least one of the housing and the plunger comprises an element of incremental resistance disposed near at least one of an upper end of a pump stroke and a lower end of the pump stroke to increase the axial load, moving the plunger upward and downward in a pumping cycle within the housing between the upper end of the pump stroke and the lower end of the pump stroke to facilitate the extraction of fluid from the wellbore, creating a dynagraph of an axial load profile on the production string throughout the pumping cycle using at least one axial load measurement, and deter mining a downhole position of the plunger within the pump housing using the dynagraph and an increased axial load measurement at a point during the pumping cycle.

In yet another aspect, embodiments disclosed herein relate to a pumping apparatus including a pump housing, a plunger operatively coupled to a terminal end of a production string and configured to move upward and downward within the pump housing, a surface pumping unit operatively connected to an upper end of the production string, and at least one element of incremental resistance disposed on an inner surface of the pump housing or an outer surface of the plunger proximate an upper or lower limit of a pump stroke.

Other aspects of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-1B show a conventional pumping system.

FIGS. 2A-2C show an apparatus for pumping fluid in accordance with one or more embodiments of the disclosure.

FIG. 3 shows a flow chart in accordance with one or more embodiments of the disclosure.

DETAILED DESCRIPTION

Specific embodiments of the disclosure will now be described in detail with reference to the accompanying figures. Like elements in the various figures are denoted by like reference numerals for consistency.

In the following detailed description of embodiments of the disclosure, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

In general, embodiments of the disclosure provide a method and system for pumping fluid from a wellbore. In one aspect, embodiments of the disclosure provide a method and apparatus for pumping fluid from a wellbore using a production string operatively connected to a plunger. In another aspect, embodiments disclosed herein relate to a method and system for pumping fluid from a wellbore using a production string operatively connected to a plunger, including a method and system for monitoring downhole location of the plunger during the pumping.

Plungers in pump systems that use production strings, for example, hollow rod strings or coiled tubing strings, to reciprocate the plunger move asynchronously with the surface pump. This occurs due to the elastic nature of the hollow rod strings and coiled tubing strings. Such elastic behavior of the rod strings and/or coiled tubing strings, including stretching and/or compression under axial loads, makes it challenging to accurately determine the downhole plunger location during the pumping.

Load cells and/or strain gauges may be installed to measure the axial load on the production string at any point in time according to embodiments disclosed herein. The axial load may include, for example, the weight of the fluid pumped via the plunger and any wall resistance between the plunger and the housing. As the plunger reciprocates within the pump housing, the axial load profile (i.e., “dynagraph”) for the production string throughout the pumping cycle can be generated. Thus, any resistance to the plunger motion within the pump housing can be observed at the surface. Once a dynagraph model is generated, an instantaneous downhole location of the plunger may be determined based on the model using the load cell and/or strain gauge readings.

In particular, one or more elements of incremental resistance may be provided as the plunger moves towards the intended upper and lower ends of the pump stroke according to embodiments disclosed herein. Thus, as the plunger nears the top or bottom of the housing during a pump stroke, the element(s) of incremental resistance may engage each other, the housing, or the plunger in order to produce the incremental resistance. Such engagement(s) generating the incremental resistance may be registered on a dynagraph, thereby indicating the position of the plunger within the housing.

In some embodiments, such element(s) may include one or more engagement surfaces. For example, one or more engagement surfaces may be positioned along one or more of an inner diameter of the pump housing and an outer diameter of the plunger. As the engagement surface contacts the pump housing, the plunger, or another contact surface at the upper and the lower ends of a pump stroke, incremental resistance is generated. Such incremental resistance may be measured as an incremental axial load on the production string, for example, using a load cell or a strain gauge.

FIGS. 2A-2C show embodiments of an apparatus for pumping fluid in accordance with the present disclosure. Specifically, FIGS. 2A-2C all show an apparatus (200) for pumping fluid in a wellbore that includes a production string (202), a housing (204), and a plunger (206). The terminal end of production string (202) may be operatively connected to the plunger (206) located within the housing (204). The upper end of production string (202) may be connected to a surface pumping unit (not shown), for example, a beam pump. In some embodiments, production string (202) may be coiled on a large spool at the surface (not shown). As the surface pumping unit moves in a reciprocating motion, the plunger (206) may be reciprocated between an upper end and a lower end of the pump stroke within the housing (204) via the production string (202) in order to pump fluid. The reciprocating motion of the plunger (206) within the housing (204) generates resistance which can be measured as axial load on the production string (202) using load cells and/or strain gauges at the surface (not shown). As discussed in more detail below, one or more elements of incremental resistance may be provided as the plunger moves towards the intended upper and lower ends of the pump stroke according to embodiments disclosed herein. Various embodiments for such element(s) of incremental resistance are further discussed below.

Referring now to FIG. 2A, where like numerals represent like parts, one or more elements of incremental resistance (208) may be placed along the inner diameter of the housing (204) near the upper and lower ends of pump stroke, respectively, according to embodiments disclosed herein. One of ordinary skill in the art will recognize that various types and forms of incremental resistance (208) along the inner diameter of the housing (204) may be used, as described in more detail below.

Referring now to FIG. 2B, where like numerals represent like parts, the one or more elements of incremental resistance (208) may be placed along the outer diameter of the plunger (206), according to embodiments disclosed herein. Further, one or more elements of incremental resistance (210) may be placed along the inner diameter of the pump housing (204), according to embodiments disclosed herein. The one or more elements of incremental resistance (208) may contact the one or more elements of incremental resistance (210) to generate the incremental resistance to the motion of plunger (206) inside pump housing (204). One of ordinary skill in the art will recognize that various types and forms of incremental resistance (208) along the outer diameter of the plunger (206) and incremental resistance (210) along housing (204) may be used, as described in more detail below.

Referring now to FIG. 2C, where like numerals represent like parts, the one or more elements of incremental resistance (208) placed along the outer diameter of the plunger (206) and the one or more elements of incremental resistance (210) placed along the inner diameter of housing (204) may have various forms, according to embodiments disclosed herein. For example, element(s) of incremental resistance (208) and/or element(s) of incremental resistance (210) may have a “wave profile,” including a series of bumps and grooves. One of ordinary skill in the art will recognize that various types and forms of incremental resistance (208) along the outer diameter of the plunger (206) and incremental resistance (210) along housing (204) may be used, as described below.

In other embodiments, the engagement surface may include at least one of a restricted inner diameter of the pump housing and an expanded outer diameter of the plunger. For example, at least a portion of the pump housing at or near the upper and/or lower ends of the pump stroke may have a restricted inner diameter. Thus, as the plunger contacts such an engagement surface at the upper and/or lower end of the pump stroke, incremental resistance between the plunger and the engagement surface may be generated. Similarly, at least a portion of the plunger may have an expanded outer diameter as the engagement surface. Thus, when this engagement surface contacts the inner wall of the pump housing, incremental resistance between the pump housing and the engagement surface may be generated.

In some embodiments, the restricted inner diameter of the pump housing and/or expanded outer diameter of the plunger may be formed along the entire circumferential surface of the housing and/or the plunger. In other embodiments, the reduced inner diameter and/or the expanded outer diameter may be formed by one or more of raised surfaces, projections, protrusions, and series of bumps and grooves, disposed at select positions along the circumferential surface of the housing and/or the plunger.

Several embodiments for installing such element(s) of incremental resistance in downhole pump systems may be used. In some embodiments, the one or more elements of incremental resistance may include a separate insert. For example, a separate insert may be installed along one or more of the inner diameter of the pump housing and the outer diameter of the plunger in order to restrict the clearance between the pump housing and the plunger, thereby producing incremental resistance. Such insert may be of the same or of a different material as the pump housing and/or the plunger. Each insert may include one or more engagement surfaces for generating the incremental resistance. For example, each insert may include one or more areas of restricted inner diameter on the pump housing. Similarly, each insert may include one or more areas of expanded outer diameter on the plunger.

Various mechanisms for attaching each insert to the pump housing or the plunger, as known in the art, may be used. In some embodiments, an insert may be welded to the inner surface of the pump housing or the outer surface of the plunger. In other embodiments, the insert may be close-fitted using a threaded connection along the inner surface of the pump housing or the outer surface of the plunger. In yet other embodiments, the insert may be installed along the inner surface of the pump housing or the outer surface of the plunger using a tongue-and-groove arrangement. In still other embodiments, the insert may be attached using a mechanical fastener device. In still other embodiments, the insert may be attached as a collar, a ring, or a scaling element. One of ordinary skill in the art will recognize that other mechanisms for attaching the insert to the pump housing or the plunger may also be used.

In other embodiments, the one or more elements of incremental resistance may form a single-piece component with one or more of the inner surface of the pump housing and the outer surface of the plunger. Such element(s) of incremental resistance may be integrally-formed with the inner surface of the pump housing or the outer surface of the plunger. For example, the element(s) of incremental resistance may be machined from the same piece of metal bar stock, thus forming a single-piece component. Such single-piece component may be installed into the pump assembly either in the shop or in the field.

In some specific embodiments, the one or more elements of incremental resistance may include one or more internal seal elements. For example, the one or more internal seal elements may be spaced along the upper and/or lower portions of the inner diameter of the pump housing, near or at the upper and/or lower ends of the pump stroke. In other specific embodiments, the one or more internal seal elements may be placed along the outer diameter of the plunger. In one embodiment, a single internal seal ring may placed along an upper and a lower portion of the inner diameter of the pump housing. In another embodiment, two internal seal rings may be placed at each of the upper and the lower portions of the inner diameter of the pump housing. In yet another embodiment, three or more internal seal rings may be placed at each of the upper and the lower portions of the pump housing.

In yet other specific embodiments, the element(s) of incremental resistance may include a combination of one or more internal seal elements and one or more of the restricted inner diameter of the pump housing and the expanded outer diameter of the plunger. For example, the internal seal elements may contact each other, the restricted inner diameter of the pump housing, and/or the expanded outer diameter of the plunger during the upper and/or lower ends of the pump stroke in order to generate incremental resistance.

In still other specific embodiments, the restricted inner diameter of the pump housing and/or the expanded outer diameter of the plunger may have a “wave profile.” Such “wave profile” may be a series of bumps and grooves protruding from the surface of the pump housing or the plunger. For example, the restricted inner diameter of the pump housing having a “wave profile” (see, e.g., FIG. 2C) may contact an internal seal element positioned along the outer diameter of the plunger to generate the incremental resistance during the motion of the plunger. As the seal element engages each groove of the pump housing having a “wave profile,” one or more distinct increments of resistance may be generated, thereby indicating the position of the plunger within the housing. Also, for example, the expanded outer diameter of the plunger having a “wave profile” may contact an internal seal element positioned along the inner diameter of the pump housing to generate the incremental resistance during the motion of the plunger. Similarly, as the seal element engages each groove of the plunger having a “wave profile,” one or more distinct increments of resistance may be generated, thereby indicating the position of the plunger within the housing.

Such incremental downhole resistance between the plunger and the housing may be measured at the surface using the load cells and/or strain gauges installed on the production string, as discussed above. For example, the incremental resistance generated during the engagement of the one or more element(s) of incremental resistance may be incorporated into the dynagraph model for the entire pumping cycle. Comparing the instantaneous resistance readings as the axial load on the production string to the dynagraph model for the entire pumping cycle can be used to determine the instantaneous position of the plunger within the housing.

FIG. 3 shows a method for using a pumping system in accordance with one or more embodiments disclosed herein. More specifically, FIG. 3 shows a method for using a pumping system including monitoring the plunger location during the pumping. Initially, the housing may be inserted into the wellbore (ST 400). Next, the rod string or coiled tubing string, which includes the plunger affixed to a terminal end, may be inserted into the housing (ST 402). Alternatively, the rod string or coiled tubing string and the plunger may be inserted into the housing at the surface, and subsequently, the housing including the plunger may be inserted into the wellbore. Optionally, the surface pumping unit configured to move the production string and the plunger upward and downward may pre-configured to limit the pumping stroke of the plunger (ST 404). That is, the amplitude (or stroke length) of the plunger may be limited by configuring settings on the surface pumping unit such that the surface pumping unit does not move the plunger past an upper end of the stroke or below a lower end of the stroke. The surface pumping unit may then move the plunger in a reciprocating motion, upward to the upper end of the stroke, and downward to the lower end of the (ST 406). As a further option, the grip of the surface pumping unit may be adjusted along the length of the rod strong or coiled tubing string (ST 408) in order to adjust the upper and the lower end of the pump stroke position.

Further, one or more load cells and/or strain gauges may be installed on the production string to measure the axial load generated on the production string at the surface (ST 410). For example, the one or more load cells and/or strain gauges may be used to measure the resistance between the plunger and the housing and/or the weight of the fluid in the plunger. One or more element(s) of incremental resistance may be provided at the upper and/or lower ends of the pump stroke (ST 412). For example, such incremental resistance may be measured as axial load by the installed load cell(s) and/or strain gauge(s). A dynagraph model showing the axial load profile on the production string throughout the pumping cycle may be created using the axial load measurements (ST 414). Using such dynagraph model and an instantaneous axial load measurement may then be used to determine the downhole location of the plunger with respect to the pump housing (ST 416). For example, assuming that the axial load on the hollow rod string or coiled tubing string at each physical plunger location along the housing does not change from one cycle to the next, the downhole plunger location may be accurately determined using the dynagraph model. Further, as the pumping conditions change, the dynagraph model can be continuously updated in order to better approximate the pump system behavior.

Advantageously, embodiments of the present disclosure provide a system and a method for pumping fluid from a wellbore using a production string, including a method and system for monitoring downhole location of the plunger during the pumping. Field tests and existing models fail to accurately determine the downhole location of the plunger in such pump systems due to the elastic nature of the rod string or coiled tubing string. Using load cells and/or strain gauges to measure axial load on the rod string or coiled tubing string and to create a dynagraph model according to embodiments disclosed herein provides a robust and accurate way to determine the downhole plunger location.

Additionally, an advantage of using one or more elements of incremental resistance in plunger and/or housing arrangements according to embodiments disclosed herein is the ability to accurately determine when the plunger has reached the upper and/or lower end of the pump stroke. For example, the one or more elements of incremental resistance according to embodiments disclosed herein may be measured using the one or more load cells and/or strain gauges. Such measurements may be incorporated into the dynagraph model and to indicate when the plunger has reached the upper and/or lower end of the stroke, based on the dynagraph model.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims. 

1. A system for pumping fluid, comprising: a production string having an upper end and a lower terminal end; at least one strain gauge for measuring an axial load on the production string; a pump housing comprising a plunger fixed to the lower terminal end of the production string, wherein the plunger is configured to move upward and downward within the pump housing in a pumping motion; a surface pumping unit operatively connected to the upper end of the production string, wherein the surface pumping is configured to move the plunger within the pump housing in the pumping motion between an upper end of a pump stroke and a lower end of a pump stroke; and at least one element of incremental resistance for increasing the axial load near at least one of the upper end of the pump stroke and the lower end of the pump stroke.
 2. The system of claim 1, wherein the production string comprises at least one of a hollow rod string and a coiled tubing string.
 3. The system of claim 1, wherein an amplitude of the pump stroke is adjusted by modifying parameters of the surface pumping unit.
 4. The system of claim 1, wherein the upper end of the pump stroke and the lower end of the pump stroke are adjusted by adjusting a grip of the surface pumping unit along a length of the production string.
 5. The system of claim 1, wherein the at least one element of incremental resistance comprises at least one engagement surface positioned along at least one of an inner diameter of the pump housing and an outer diameter of the plunger.
 6. The system of claim 5, wherein the engagement surface comprises at least one of a restricted inner diameter of the pump housing and an expanded outer diameter of the plunger.
 7. The system of claim 5, wherein the engagement surface comprises a separate insert positioned along the at least one of the inner diameter of the pump housing and an outer diameter of the plunger.
 8. The system of claim 5, wherein the engagement surface comprises a single-piece component with the at least one of a restricted inner diameter of the pump housing and an expanded outer diameter of the plunger.
 9. The system of claim 5, wherein the engagement surface comprises at least one internal seal ring.
 10. The system of claim 5, wherein the at least one element of incremental resistance comprises a combination of a restricted inner diameter of the pump housing and an expanded outer diameter of the plunger.
 11. The system of claim 6, wherein the restricted inner diameter of the pump housing comprises a wave profile.
 12. A method for pumping fluid from a wellbore using a pumping system, the method comprising: inserting a housing comprising a plunger coupled with a production string into the wellbore, wherein at least one of the housing and the plunger comprises an element of incremental resistance disposed near at least one of an upper end of a pump stroke and a lower end of the pump stroke to increase the axial load; moving the plunger upward and downward in a pumping cycle within the housing between the upper end of the pump stroke and the lower end of the pump stroke to facilitate the extraction of fluid from the wellbore; creating a dynagraph of an axial load profile on the production string throughout the pumping cycle using at least one axial load measurement; and determining a downhole position of the plunger within the pump housing using the dynagraph and an increased axial load measurement at a point during the pumping cycle.
 13. The method of claim 12, further comprising installing at least one strain gauge for the at least one axial load measurement on the production string.
 14. The method of claim 12, wherein the production string comprises at least one of a rod string and a coiled tubing string.
 15. The method of claim 12, wherein the at least one element of incremental resistance comprises at least one engagement surface positioned along at least one of an inner diameter of the housing and an outer diameter of the plunger as the at least one step of incremental resistance.
 16. The method of claim 12, wherein the at least one element of incremental resistance comprises at least one of a restricted inner diameter of the housing and an expanded outer diameter of the plunger as the at least one step of incremental resistance.
 17. The method of claim 15, wherein the at least one engagement surface comprises at least one internal seal ring.
 18. The method of claim 16, wherein the restricted inner diameter of the housing comprises a wave profile.
 19. A pumping apparatus comprising: a pump housing; a plunger operatively coupled to a terminal end of a production string and configured to move upward and downward within the pump housing; a surface pumping unit operatively connected to an upper end of the production string; and at least one element of incremental resistance disposed on an inner surface of the pump housing or an outer surface of the plunger proximate an upper or lower limit of a pump stroke. 